1. Field of the Invention
The present invention is in the field of hydraulics and more specifically relates to an hydraulic positioner for maintaining a given separation between its attachment points which has a bidirectional detenting action whereby the given separation can be altered only by application of a sufficiently large overriding force.
2. The Prior Art
Unlike shock absorbers, which are operative only when in motion, the present invention remains stationary between successive alterations. The present invention includes two attachment points whose separation is selectively alterable by application of a force in excess of a predetermined magnitude. As long as the predetermined magnitude of force is not exceeded, the device of the present invention provides a rigid connection between its two attachment points. From a first given separation, the attachment points can be selectively spread more widely apart or can be drawn more closely together, but not alteration can be made unless the applied force exceeds the predetermined magnitude. Thus, the present invention exhibits a bidirectional detenting action from any given separation.
In contrast to the present invention, the invention disclosed by Ackerman in U.S. Pat. No. 3,236,515 exhibits a locking action rather than a detenting action. When Ackerman's device is locked, no amount of force will alter the separation between the attachement points. When Ackerman's device is unlocked, it will not maintain a given separation between the attachment points if a measurable force is applied to the attachment points.
In U.S. Pat. No. 3,228,632, issued Jan. 11, 1966 to Hunth, a different form of lock is described. That device includes a piston movable within a cylinder by piston rods extending in opposite directions from the piston. One side of the piston is called the inlet side and the other side of it is called the outlet side. The device is set to transmit movements of varying amplitude and direction from the inlet piston rod to the outlet rod while preventing reaction forces applied to the outlet rod from being transmitted to the inlet rod. In contrast with the present invention, the Hunth device lacks a reservoir and employs a different system of valving.
In U.S. Pat. No. 2,782,877 issued Feb. 26, 1957 to Crabtree, there is shown a shock absorber in which the rate of movement is controlled by opposed flapper valves. The flappers are resiliently deformable, and the construction of the flapper valve is such that the application of any measurable force will result in some fluid flow. Consequently, the Crabtree device is incapable of maintaining a fixed separation between its attachment points when forces less than a predetermined magnitude are applied. Crabtree shows a reservoir which is pressurized by the compression of air which partially fills the reservoir. Transfer of fluid from the reservoir to one of the working chambers is controlled by a preloaded ball check valve.
In U.S. Pat. No. 2,487,472 issued Nov. 8, 1949 to Patriquin, and in Canadian Pat. No. 587,934, issued Dec. 1, 1951 to Whisler, Jr. there is shown a check valve in which an O-ring forms a seal between a surface of a piston and the cylinder wall. Both of these devices differ markedly in structure and operation from the present invention. Neither of these inventions will maintain a fixed separation between its attachment points when any measurable force is applied in one of the two directions.
In a copending application, Ser. No. 761,908 filed Jan. 24, 1977, the present inventor, John Kourbetsos, has disclosed a hydraulic snubber in which a check valve employing an O-ring is used for limiting the rate of motion in one direction while alternately permitting unlimited rate of motion in the opposite direction. Clearly, that device cannot be used to maintain a fixed separation between its attachment points.
Thus, it appears that none of the prior art inventions described above operate in the same manner as the present invention, and in addition, the present invention can be distinguished on the basis of its structure.
The prior art does not disclose a hydraulic positioner for maintaining a given separation between its attachment points and exhibiting a bidirectional detenting action whereby it rigidly maintains the given separation until the separation is altered by application in either direction of an overriding force greater than some predetermined magnitude. The present invention further includes a pressurized reservoir for replacing any fluid lost by leakage. Thus, it appears that the present invention fills a long-standing deed for a device of its kind, and should prove valuable in such diverse applications as supporting the hoods of automobiles and trucks, positioning lamps and illuminators, and providing steady support for positioning apparatus used by a dentist.